Transcript A Wakeup Scheme for Sensor Networks: Achieving Balance

A Wakeup Scheme for Sensor
Networks: Achieving Balance between
Energy Saving and End-to-end Delay
Xue Yang and Nitin H. Vaidya
University of Illinois at Urbana-Champaign
IEEE RTAS 2004
May 26, 2004
Problem Statement

Sensor networks have limited energy
supply

Two different ways to exploit the energy
saving
 Spatial
redundancy
 Temporal energy saving
 Wakeup
schemes
Problem Statement

Wakeup schemes
 have
great potential in energy saving
 incur wakeup delay, which can lead to long
message delay.

Focus of this paper:

Achieve the balance between energy
saving and end-to-end delay
Related Work

STEM (Sparse Topology and Energy
Management) [appeared in mobihoc’02 by
Schurgers et al ]
 Two radios, wakeup radio and data radio, have the
same power consumption characteristics and
channel bit rate
 A node periodically wakes up to listen to the
wakeup radio, and keeps awake upon receiving a
wakeup packet intended for itself.
 The wakeup packets are sent by some nodes that
have packets to send.
STEM
awakened
Twack
Sender
Tw
Twack
Tw
Twack
Tw
Tw
T
Receiver



Duty Time (Td)
sleep
Duty Time (Td)
Wakeup delay largely depends on T
Energy saving is determined by the duty ratio of T/Td
Td, which equals to 2Tw + Twack, depends on the
wakeup radio bit rate.
Wakeup Delay of STEM

To achieve a ten-fold decrease of energy
consumption, the wakeup latency is about 1.3 s
per hop, using a wakeup radio with bit rate of 2.4
Kbps.

The end-to-end delay only due to wakeup delay
is as large as 13 s if the message needs to be
forwarded 10 hops.
Network stack of wakeup schemes
Access delay
Packet delay
Transmission delay
Proposed solution
to reduce end-to-end delay

Pipelined Wakeup:
 Pipeline
the wakeup procedure with the
packet transmission to hide the wakeup
delay.
Wakeup delay
Wakeup next hop node
Wakeup next hop node
Wakeup next hop node
Packet delay
Transmit packet
Transmit packet
Problems need to be addressed

Which node is on the packet forwarding path
and should be awakened in advance?

Wakeup delay should be less than packet delay
so that it can be effectively hidden. Under such
a constraint, how to retain sufficient amount of
energy saving?
Pipelined Tone Wakeup (PTW)

Which node is on the packet forwarding path
and should be awakened in advance?


Wakeup all one-hop neighbors.
How to retain sufficient amount of energy saving
while hiding most of the wakeup delay?
PTW (cont.)

Which node is on the packet forwarding path
and should be awakened in advance?


Wakeup all one-hop neighbors.
How to retain sufficient amount of energy saving
while hiding most of the wakeup delay?
 Duty
Ratio T/Td determines the energy saving.
 Reduce the duty time Td of each node using wakeup
tones instead of wakeup packets
Probability of correct detection
Wakeup Tone Detection Time
Wakeup tone detection time (us)
(Comply to the design guidelines of RF Monolithics TR1000)
PTW (cont.)

Advantages of using wakeup tone in PTW:


All one-hop neighbors can be awakened by sending
a wakeup tone
A shorter duty time is needed for each node, which
can help to retain the energy saving under the
constraint for wakeup delay.
Duty time 1
Wakeup period T
Duty time 2
Wakeup period T
PTW (cont.)

Disadvantage of using wakeup tone:


Not only the intended receiver but all the one-hop
neighbors around the sender will be awakened
Energy wastage caused by unnecessary
wakeup should be reduced as much as possible.

Transmit short notification packets before data
packets
Example of PTW
Analysis for Energy Consumption

Objective: Identify the condition under which the
proposed PTW scheme can show improvements on
energy saving, while using pipelining to reduce the
end-to-end delay.
Sender:
“monitoring state”
Tevent
Turn off radio
Initiate wakeup
procedure
duty time Td
Receiver:
T
Turn off radio
T
T
Duty Ratio: Duty = T / Td
T
React to
wakeup
Wakeup Procedures of STEM and PTW
STEM
Twack
Sender
Tw
awakened
Twack
Tw
Twack
Tw
Tw
T
Receiver
sleep
Duty Time (Td)
Duty Time (Td)
PTW
Send wakeup tone
Sender
T
Receiver Duty Time
(Td)
awakened
sleep
Duty Time
(Td)
Result of Analysis

A loose bound: the proposed PTW
scheme can save more energy when
the following constraint is satisfied:
Result of Analysis


When Dutystem = 10 and Dutytone = 100,
Tevent > 21 T is sufficient.
Constrained by the wakeup delay, T
cannot be too large. Assume T = 1s,
then Tevent > 21 s can be easily satisfied
by many sensor network applications.
Performance Evaluation
Radio Power Consumption (TR1000)
Simulation Results
Results for random networks
Dutystem=5.33
NPM
Dutystem=13.33
PTW
(S)
Results for random networks
Dutystem=13.33
Dutystem=5.33
PTW
NPM
Conclusion

A pipelined tone wakeup scheme is
proposed for sensor networks


An asynchronous wakeup pipeline is
constructed to overlap the wakeup
procedures with packet transmissions.
An end-to-end delay close to the case
without power management can be
achieved while a major energy saving can
be obtained.
Thank you!
Backup Slides
Traffic prediction

Chunyu Hu and Jennifer C. Hou, LISP:
a link-indexed statistical traffic
prediction approach to improving
IEEE 802.11 PSM, in Proc. of IEEE
Int'l Conf. on Distributed Computing
Systems (ICDCS'04), March, 2004.